text:
Can the measured thrust of a propeller be greater than the max thrust predicted by Froude's theory?
Can the measured thrust of a propeller be greater than the maximum possible thrust predicted by Froude's Propeller Theory?
Is Froude's theory reliable in practice regarding the upper limit of the thrust delivered by a propeller of diameter, d, turned by an engine that absorbs the power, P?
I get the measured thrust of a 26 inch, 2 blades propeller, higher than what Froude's theory predicts.

No.
The actuator disc theory for Propellers uses some simplifications, which are grouped into a propeller efficiency factor which normally is between 0.7 and 0.9. This accounts for friction and swirl losses, which are both neglected but very real. Also, the theory assumes equal speed over the stream tube and an infinitesimally small hub, both of which increases efficiency over that of real propellers.
If the propeller uses a large duct, Froude's actuator disc theory would be insufficient to explain all thrust. You might want to explain your measurements in more detail to get a better answer.

Can the measured thrust of a propeller be greater than the maximum possible thrust predicted by Froude's Propeller Theory?

It might seem incredible but the answer looks to be: yes it can.
"Stoddard [1977] reports measured values of the thrust which exceed the theoretical upper limit as predicted by the momentum theory by 20% to 50%."
Source: ON THE LIMITATIONS OF FROUDE'S
ACTUATOR DISC CONCEPT,
G.A.M. VAN KUIK. page 7.
Update
"For the propeller flow the momentum theory underestimates the induced velocity, while for the wind turbine flow this is overestimated. As the induced velocity has a different sign in both flow regimes, the total velocity at the disc $u_d = U_0 + u_i$ is underestimated in all flow states: the mass flow through the rotor is always higher than predicted by the classical momentum theory."

Source: the same paper as above.

The paper is on wind turbines, and "thrust" is actually drag. Of course the drag of a wind turbine is higher than predicted by actuator disc theory in off-design conditions. Where propellers show higher thrust than predicted, the author says "This actuator disc concept bas been developed for rotors making use of concentrators like shrouds or tipvanes. These devices increase the flow through the rotor in an artificial way."

That paper treats all cases, wind-turbines, propellers, rotors in hover, see the diagram from page 4 (https://pure.tue.nl/ws/files/3577374/345682.pdf).


text:
What is weight-climb speed?
I have a question about a document published by the Association of European Airliners. The name of the document is “Long Range Aircraft - AEA Requirements.” In the Appendix titled "Definitions and Inputs for Range and DOC Calculation," paragraph 1.1 (“Flight Profile for DOC and Range Calculation”) at Note c) we can read the following recommendation:

Cruise, and completion of step, shall be at that altitude at which the potential rate of climb, at initial cruise weight-climb speed, is 500 ft./min or more

I don't understand the meaning of that sentence. What’s the definition of “weight-climb speed?”

DeltaLima gave you a precise, well worded answer to your question. If you are further interested in the subject, I would invite you to ask a follow on question, something like, why is it not a good idea to climb higher than a level at which you would have a cruise weight-climb speed less than 500 ft/min

A cruise weight-climb is a climb segment during the cruise phase of the flight to achieve a higher flight level that was previously not reachable due the weight of the aircraft.
Long range aircraft cannot climb as high initially because of the weight of the fuel they carry. Their operating ceiling is power limited. As the aircraft burns off weight during the flight, the drag decreases and gradually excess power becomes available for climbing.
This recommendation is not to start climbing to the next level until a vertical climb speed of 500ft can be maintained at the new level, at the initial cruise speed after that weight-climb.
For example, if the the cruise starts at FL270, and one wants to climb to FL290 for a cruise at Mach 0.80, the weight-climb should not start before the aircraft can maintain a 500 ft/min climb at Mach 0.80 at FL290.

Separate questions should be asked separately, and it was

source: Stack Exchange

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sort: votes


text:
How does airfoil thickness affect the Mach number at which it experiences transonic flow?
Roskam (book: Airplane Aerodynamics and Performance, Subparagraph: 2.5.2 HIGH-SPEED AIRSPEED INDICATORS (COMPRESSIBLE FLOW)) affirms:

[...] Airplane with no sweep and thick airfoils become transonic at much lower flight Mach numbers than airplanes with significant sweep and thin airfoils. [...]

Question: How does airfoil thickness affect the Mach number at which it experiences transonic flow?

The displacement effect causes the flow around a thick body to speed up more than around an equivalent but thinner body. The thicker body pushes the air aside and around itself more, causing the flow to accelerate relative to the vehicle and to become supersonic at a lower flight Mach number.
Wing sweep has a similar effect, as only the orthogonal speed component will be affected by the wing and the effective Mach number of all thickness-, camber- and angle-of-attack-related effects is reduced by the cosine of the sweep angle. Again, the displacement effect will be reduced by sweep.

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text:
Where to find the various cargo hold dimensions and volumes of transport aircraft, such as the A330-300?
What are the dimensions of the cargo hold on the Airbus A330-300? (In order to check the usable space for containers or baggage.)
I'm looking for the internal dimensions of the hold with its subsections in the Airbus A330-300, i.e. length, width and height. What are they? This is in order to understand how much space there is and and how it's divided for standard containers or for baggage in bulk configuration.
I'm looking the value of volumes of the parts of the hold, too.

Where did you look yourself and what information was lacking?

As for the widths, they are shown in this document from Air China

source: Wikipedia
They make the holds to fit the standard containers. They fit fairly tight but there's a little room around them.

source
The outside height of an LD3 is 162.6 cm. If you look at the top diagram, on the right you see they have that marked (as 163 cm), therefore 171 is the height of the hold itself. There is 8cm of clearance above. On the left, PAG and PMC are pallets, or "cookie sheets". You stack whatever you need on them and cover it with a net, so 171cm would be the limit to how high you can load it so that it fits into the hold, except that the document lists the door on the front cargo hold to be 170cm and the aft to be 168 cm. So whatever you stack on a pallet has to fit through the door.
The bulk cargo hold is an irregular shape, so exact dimensions won't be given. But that Air China document indicates that they are 511cm deep and have a volume of 19.7 cubic meters.

Thank you TomMcW; finally, it's something with measures I'm looking for, i.e. internal of hold; only here it seems to me what we are seeing in this figure measured "171 cm" is not refered to cargo hold too, or I'm an in error and it's height of internal of structure.... ???

I'm looking a reference with value of volumes of forward and aft cargo hold, too

@d.pensopositivo I would guess that the 171cm dimension is the height of the door, while the max height of cargo (including a pallet, if it's on one) would be 163cm. Terry gave you some search terms on his comment on ymb1's answer that may well get you all the details you're after, since we don't seem to be able to get them specific enough for you.

Edited for clarification

@FreeMan Thanks for pointing out the door. That limits things by a few more cm

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text:
What are the effects of headwind on ground speed and take off run?
I'm just making sure I got this right.
For the take-off roll, having headwind is preferable, so there is a positive airspeed.
For the en-route segment, a headwind is not ideal and increases time to destination, whereas a tailwind is more favorable.

Yes, that is about right. Is there a question?

So you are asking if what you are thinking is correct?

You're doing it wrong.

@RyanMortensen: How should your comment be understood unless you explain what is wrong? I see two correct statements here (head wind for landing and tail wind for cruising are usually seen as positive by the pilot)

@mins you're being too literal.  Forget I said anything...  I was referring to how to ask questions.  Not the statements contained.

Short Answer: Yes, you have it right.
For a longer answer consider an example aircraft that has the following characteristics:

Takeoff Speed: 60 knots (Indicated Airspeed)
Landing Speed: 50 knots (Indicated Airspeed)
Cruise Speed: 100 knots (Indicated Airspeed)

Note that all the speeds are airspeeds, which are what we usually measure in flight.
To find the groundspeed you add or subtract the effect of wind, which will become important as you'll see:

A headwind gives the plane a lower groundspeed for a given airspeed.
If our example airplane has a 10-knot headwind it has the following practical effects:

On takeoff the aircraft only has to gain an additional 50 knots to reach takeoff speed:
It effectively has a 10-knot "bonus" from the headwind, and will thus reach takeoff speed in a shorter distance, and need less runway.
Once in the air the headwind works against the aircraft's progress: The groundspeed of the aircraft is equal to its airspeed minus the headwind, so while you're cruising at 100 knots airspeed you're only making 90 knots over the ground. A 100-mile flight will take an extra 7 minutes to complete.
On landing the aircraft will arrive at the runway with a 50-knot indicated airspeed, but because of the headwind will be making 40 knots across the ground. It will thus have less energy to get rid of once it lands, and will require less runway to slow to a stop.

A tailwind gives the plane a higher groundspeed for a given airspeed.
If we reverse our earlier example and give the aircraft a 10-knot tailwind it has the following effects:

On takeoff the airplane must accelerate to a 60-knot airspeed, however it's also being pushed along by a 10-knot tailwind, so it effectively has a -10 knot airspeed standing still: The wind is blowing forward over the wings. When it reaches its 60-knot takeoff speed it will have a 70-knot groundspeed because it's being pushed along by the wind, so it will have a longer takeoff roll.
In cruise the wind continues pushing our example airplane along, so its 100-knot cruise speed gives it a 110-knot ground speed. A hypothetical 100-mile trip would take a little over 54 minutes.
On landing the aircraft arrives with a 50-knot indicated airspeed, but a groundspeed of 60 knots (the wind is still pushing it along), so it will have more energy to dissipate when it lands: A longer ground run, and more braking required.

A chart of the effects of headwinds and tailwinds on takeoff and landing can be found in the Pilot's Handbook of Aeronautical Knowledge, it's reproduced below.

Effects of winds in cruise can be calculated using an E6B Flight Computer


text:
Why do the British not produce anymore aircraft?
Minus Airbus which is a group of companies, why does the United Kingdom not produce aircraft anymore ie, the VC10.

Good question.  I imagine that it's a combination of the high cost of labor and the fact that Airbus is sort of the de facto plane maker for Europe.  How does a new British plane manufacturer compete with Airbus when the EU will do anything to guarantee failure of any British competition?

I had a feeling the EU would be a reason behind it. It's a shame because we had plenty of home grown companies established here inc work force, factories the lot!

@acpilot The UK was a member of the EU until just recently (and actually will remain a member of it until separation is complete).  Until recent events, why would the EU "do anything to guarantee failure of any British competition"?

No it won't remain a member, that's why we voted out.

@acpilot That's complete nonsense, sorry. Very few things actually are EU conspiracies...

Who says it's just Airbus?

Maybe because the quality and the technology is not up to the standards of the market not because British are not capable but because it takes a huge economic effort to compete? Just guessing...

@david richerby.  No need to apologize.  I'm not saying it's a conspiracy.  It's all about competition and political pride.  There's nothing cloak and dagger about it.  The barriers to entry are way too high anyway.  This is all academic.

@FabrizioMazzoni Would you care to make a more reasonable guess? Because poor quality and bad technology really must be the reason that all Airbus wings are made in the UK, about 60% of the engines on Airbus planes are made in the UK, plus more than a third of the Eurofighter Typhoon and about 20% of the F-35.

@acpilot I'm not apologising. I'm expressing regret towards your attitude.

I made an observation and provided a possible reason why, aside from industrial limitations, the British cannot field a production airliner.  If I have an attitude it is one of curiosity.  I would love to be wrong and see a good western alternative to Airbus and Boeing mainliners.

@user13555 It's a more sustainable argument to say that without the EU and Airbus, the British aerospace industry would be on life support, rather than being the worlds 3rd largest that it is now.  No new designs, no capability to adjust to the explosion in air travel, a history of the right aircraft at the wrong time, no investment, stagnant manufacturing techniques firmly stuck in the 50s, no world beating aircraft ready for the 70s and beyond, no appetite on the part of the tax payer to continue to pour money into flag waving exercises and so on.  That's why we don't build aircraft anymore.

@DavidRicherby: The main reason for Airbus wings made in Britain is political. The British designs are reviewed by their partners and often need improvement. For the A310, Airbus Bremen designed a counter-proposal to shame the British into re-designing their wing (by more-or-less copying the German wing design, no less).

The root of the reason is the fact that aircraft design has become very expensive and the world economy cannot support more than a few companies anymore.
Look at other industrialized countries: They all used to have scores of aircraft companies, which all merged or went down over time. Russia might seem an exception, but the Russian design bureaus are not very productive anymore and kept alive artificially. By now, a national economy the size of Great Britain is too small to support even a single commercial jet builder.
In Augustine's Laws, Norman Augustine shows how aircraft prices have historically accelerated at a faster rate than the economy, and driving this to it's ultimate conclusion, he predicts for the US military:

In the year 2054, the entire defense budget will purchase just one
  tactical aircraft. This aircraft will have to be shared by the Air
  Force and Navy 3½ days each per week except for leap year, when it
  will be made available to the Marines for the extra day."

There is no conspiracy about it, economics is enough for a convincing explanation. If there is a culprit for the early death of many British aircraft makers, it would be the British Government bureaucracy itself, with a helping hand given by BOAC management. Britain effectively nationalized her aircraft industry at the onset of WW II, and left it to Government bureaucrats to decide which aircraft to build next. This produced aircraft like the Saunders-Roe Princess or the Bristol Brabazon which incorporated many innovations, but were conceptually completely behind their times. When they once tried to be visionary, they steered all efforts into supersonic airliners, which also proved to become a dead end.
When British designers tried to design jet airliners, BOAC management saw no market for a jet airliner but bought the Boeing 707 less than a year later. If you desire to see a conspiracy behind the early death of many British airliner projects, maybe start looking here. The EU certainly has nothing to do with it.


text:
Why do most vehicles seen at airports use slow flashing orange beacons?
Most vehicles seen at airports use slow flashing orange beacons rather than a rotating beacon, is there a purpose to this? What is the correct name?

ICAO
Mobile obstacles at airports are lighted with type C obstacle lights, this refers to airport lighting practices defined in ICAO in Annex 14:

6.2.2.6 Low-intensity obstacle lights, Type C, displayed on vehicles associated with emergency or security shall be flashing-blue and those displayed on other vehicles shall be flashing-yellow.

Rotating vs. flashing
There is no difference in rotating vs. flashing. Flashing is used with modern technologies, e.g. LED, as the number of on/off cycles has little impact on lifetime, contrary to filaments which are subject to thermal fatigue when temperature changes.
Flashing frequency
From same ICAO document:

Table 6-1. Characteristics of obstacle lights
Low-intensity, Type C (mobile obstacle): Flashing (60-90 fpm)

This choice is likely based on physiological considerations, to limit ocular fatigue, and impact of a repeating signal on brain.
Color
Red/blue are for emergency/safety vehicles, orange for support vehicles.

Source
FAA
FAA implements ICAO recommendations in AC 150/5210-5.

Airfield Service, Aircraft Support, and Airport Operations Vehicles
The standard for identification lighting is a yellow flashing light that is mounted on the uppermost part of the vehicle structure. A steady yellow light designates vehicles limited to non-movement areas. [...]

TLTVs. An LED light bar placed above the operator’s cab may be used in place of the rotating yellow flashing light. In  addition, a yellow  flashing  light  (of  any  type) must be installed on the upper left-rear and right-rear corners of the TLTV, and must be activated  when an aircraft  is in tow.

For color:

Airport Emergency Vehicles.
a. Ambulances. Per  the  most  current  version  of  Federal  Specification  KKK-A-1822.
b. ARFF Vehicles.  Red or a combination of red-and-white flashing lights per the chromaticity requirements in Appendix B.

Airport Security Vehicles.  Signal blue or a combination of red and signal blue flashing light per the chromaticity requirements in Appendix B.

Airfield Service, Aircraft Support, Airport Operations, and Other Vehicles. Yellow flashing light per the chromaticity requirements in Appendix B.

For frequency:

Lights must flash at 75 ± 15 flashes per minute

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text:
what is the use and the locations of nacelle hinge bracket?
i have seen on the webs about the additive manufacturing about this bracket here but I have no clues on where is it located and whats the purpose of it. Do give me any links if there are actually any if possible.

I'm assuming that you're talking about the part below. The part was changed from cast steel to titanium DMLS additive manufacturing technology.

Image from belement.co.il
The hinge is used to hold the engine nacelle cowling when opened. YOu can see four of them (older versions) on top of the open cowing in the image below:

Image from article.wn.com

omg thanks so much


text:
What are the reasons why we do not have VTOL commercial airliners?
I understand that there are noise issues, and that there may be an economic case dependent on stage length, but other than that I'm not quite sure why they haven't happened. Is there something technical I'm missing?
Exhaust gas re-ingestion doesn't seem to be that great an issue, it looks like you just install fences to make sure that exhaust can't get into the inlets.

VTOL is very hard to do.

also check out http://aviation.stackexchange.com/questions/11657/how-much-thrust-is-needed-by-an-aircraft-to-have-vertical-takeoff/11662#11662

@ratchetfreak I think that the thrust limitation ting is a bit of a non-argument, given the much higher thrust density possible with electric ducted fans. Is there something else I am missing?

What makes you think it would be desirable?

Commercial airliners are significantly larger, and therefore heavier, than aircraft with use V/STOL. Because of that, it would take more fuel and engine power to run that airplane, driving up the cost of running it. There are also many other airframe stress and balance factors that come into play when doing VTOL.
If you are including turbo-prop airliners in your definition of airliners, they could do V/STOL with a configuration like the V-22 Osprey because they are small enough.

First, we have to decide what kind of VTOL we are going to use- tiltrotor like Augusta WestlandAW609, compound helicopters like Eurocopter X3 or using jets like the F-35.
For commercial operations, the first two are not very suitable as they lack the speed and carrying capacity. At best, they can act as costly and complicated propeller aircraft, which are not the main type in use. So, lets consider the jet aircraft.
Actually, there was a vertical takeoff jet transport, the Dornier Do 31. It is instructive to consider what happened in this case. It never got past the prototype stage.

"Dornier Do 31 in 1968" by Ralf Manteufel - http://www.airliners.net/photo/Germany---Air/Dornier-Do-31E/1265410/L/. Licensed under GFDL 1.2 via Commons.

For takeoff, the VTOL aircraft has to produce quite a large amount of thrust- Do 31 used a grand total of 10 engines, including 8 exclusively for vertical takeoff. The engines produced a total thrust in excess of 290kN for lifting the 27 ton aircraft (not at its MTOW). In contrast, the 50 ton Boeing 737-100 had engines that produced a sum total of 128 kN.
Even military VTOL aircraft like the Harrier and F-35 were not able to take off vertically at their full load. In fact, Harrier was rarely used operationally in VTOL mode. In most of the cases, it was operated in a rolling takeoff.
VTOL mechanisms are complicated. You've to either swivel the engine thrust (like F-35) or use separate engine(s) (like Do 31) for vertical takeoff. In either case, you're having dead weight. This increases the fuel and structure required (for support), which leads to further weight and fuel requiremetn and so on.
The fuel consumption for VTOL would be enormous. The economics is against the operation of VTOL aircraft.
More complicated the mechanism is, more chances of failure. Not a good thing in commercial operations.

As for compound helicopter, the Fairey Rotodyne was designed with commercial transport in mind; however, noise considerations (among others) killed the project. Of course, if a large rotor is used, the drag will be prohibitive at high speed.

Image from jefflewis.net
AW 609 was the first tilt rotor to be developed with commercial operations in mind. However, with the fatal crash of second prototype, it remains to be seen if it will succeed.

authors: นันทิชา โคตหงษ์


text:
Has a pilot ever been disciplined for taking a guest for a flight in a single-seat fighter aircraft?
I recall reading of a spitfire pilot who was suspended for taking a member of the WAAF up for a jaunt to impress her. She supposedly sat in the pilot's lap throughout the short flight and they were caught when they landed and a member of the ground crew noticed her alighting. I specifically remember the author referred to her as "a uniformed lovely" in his recounting.
I've spent some time googling around and rummaging in my library but to no avail. Can anyone identify this specific incident (ideally the exact account) and/or have there been other incidents that are similar?

Does anyone seriously believe that this happened only once?

@A.I.Breveleri - I guess we'll find out if/when someone posts an answer :-)

According to the book "A Spitfire Girl" the pilot's name was Flight Lieutenant Edward Gordon Brettell DFC of "Great Escape" fame, among other things, and he was court-martialed for flying his Spitfire Mark Vb of 92 Squadron to a dance with a WAAF on his lap. Squadron Leader Tony Bartley DFC helped defend him during the court-martial.
The man was a colorful character, to say the least. In one of the many references to him on the Internet I found this:

He had flown his girlfriend, a WAAF based at Tangmere, in his single
seat Spitfire to RAF Biggin Hill for a squadron party. Unfortunately
for him, the station commander who was there when they landed took a
dim view of his actions and reported him. Among the charges at his
later court martial was endangering the King's aircraft (King George
VI was then on the throne). He called upon his friend, a Battle of
Britain ace with a Hatfield-link, Anthony Charles Bartley (41816) for
help.
Tony Bartley was acting as a test pilot for Supermarine at the time.
He later revealed in his autobiography that he asked Jeffrey Quill
(Supermarine's chief test pilot) and Joseph Smith (Supermarine's chief
designer after Reginald Mitchell's death) for their help. Joe Smith
even went so far as to draw up some mathematical equations alleged to
prove the aircraft wasn't in any danger, which Bartley presented at
the court martial. Although the clinching argument was when asked by
the prosecution how he could prove it, Bartley admitted to having
committed an identical offence previously. Now faced with the prospect
of having to prosecute two badly needed officers with a war on, the
charge was dismissed. Although Gordon Brettell was transferred away
from the squadron.

Hey, he is a test pilot after all. It's his job to push the limits.

That was Bartley; Brettell was not a test pilot, he was just crazy. :)


text:
How do X-shaped control surfaces work?
I watched this video of the Raytheon SDB II and noticed that it seems to have no control surfaces on its wings, just the four fins on the tail. How do these fins work to alter the attitude of the SDB and other missiles or aircraft using the same scheme? For example, if it were to pitch downwards, which fins would need to move and in which direction?

Why is this question getting down voted? It is clear, specific, and on-topic. It is a good question!

First, the precise terms is not fins, but control surfaces. Fins would be fixed but the four rear surfaces can rotate around a spanwise axis. By rotating, they can be positioned at an angle to the airflow, thus deflecting it and creating an opposing force.
Compare that to a V-tail on an aircraft. They work in the same way by creating a force normal to their plane. While this force has a vertical and horizontal component, the horizontal components of the single surfaces cancel each other when all surfaces are rotated by the same angle. Their vertical components will add up, creating a pitching moment.
When the left and right surfaces are rotated by the opposite angle, their vertical force component will cancel while the horizontal component will add up, thus creating a yawing moment which swings the tail around.

If it were to pitch downwards, which fins would need to move and in
  which direction?

All four surfaces will move trailing edge down, so the resulting force will point up and pitch the whole craft nose down.

Finally someone answers the actual question! Glad you beat me to it; you are better at explaining these things.

The Raytheon SDB (Small Diameter Bomb) has four fins at the rear end for control of the bomb during flight.

Image from defenseindustrydaily.com
The basic operation of the fins for control is similar to the aircraft control surfaces like the stabilizer. The fins are located way from the cg so that any change in their lift will cause a moment at the cg, helping in changing the missile orientation. For example, for turning the misile, the top and bottom fins are rotated.

Image from Principles of Guided Missiles and Nuclear Weapons by USN
Note that, in case of SDB, the entire fin rotates rather than a part, but the principle is the same. For pitching up and down, the fins on either side are rotated (rotate up for pitch down and rotate down for pitch up).

Image from Principles of Guided Missiles and Nuclear Weapons by USN

A number of missiles have 'X' shaped control surfaces so as to mount on the aircraft rails so that they extend on either side of the rail. The operation is similar to what is outlined above- the deflection (rotation) of the control surfaces create pitching moment about the cg.
For 'X' shaped control surfaces, the rotation of control fins cause forces in both the horizontal and vertical axes (as opposed to the '+' shaped ones, where only two can be rotated for creating a pitching moment in one plane); Here, if all the control fins are rotated by same angle, the horizontal components cancel each other and the vertical component causes the missile (SDB) to pitch. For yaw, the surfaces are rotated in opposite directions, resulting in the vertical component being cancelled, and the horizontal components causing yaw.

The SDB seems to be closer to a V-tail than a conventional one.

Having control surfaces exclusively at the rear results in a long arm indeed - bot only for pitch and yaw. What about roll? Is coordinated flight less important for 'aircraft' like this?

Roll control is easily obtained by deflecting all surfaces in the same (relative) direction, canards can be used too.

@RobVermeulen They have some roll control, but looking at the picture it is probably not a coincidence center of lift is high with dihedral wing.

Nice graphics, but doesn't answer the question: How do the X-config control surfaces work to alter the attitude, etc

There must be fairly good roll control, as in the video demonstration, it looks like the SDB is attached to the F-15 upside down, and then rolls right side up after deploying the wings.


text:
Why are aerial taxis multirotored, instead of a single rotor?

source -- image shows Volocopter's design
I find that in the designs of aerial taxis, particularly in Volocopter's design, the design consists of a system of multirotors.
What is the main reason for not substituting this bunch of rotors with fewer bigger blades (helicopter)? As far as I know, a helicopter is energy efficient for horizontal displacement, and the multirotor is at hovering. Does a quadrotor taxi provide any other dynamics advantage?

With multirotors there is no need for complex cyclic/collective pitch regulation with swashplates. Control is achieved by means of electronic speed regulation of the individual motors. Far simpler and cheaper...

@xxavier …and lacking the capability of autorotating to land, but the fully-automatic vehicle control is not good enough to do unpowered emergency landing anyway, so reliability has to be ensured by other means.

AFAIK, none of these actually exist as anything more than computer-generated artwork.  I suspect the multi-rotor aspect is simply "cool", intended to attract investment from people whose only knowledge of aircraft construction has been playing with a drone.  (Just as they've somehow managed to develop ultra-miniaturized batteries for that machine :-))

@jamesqf, I'm happy to prove otherwise: https://evtol.news/2019/11/04/ehang-delivers/

@AnbuAgarwal Updated link (Jun 2023) https://evtol.news/news/ehang-delivers

It’s a good question. Single rotor helicopters exist already, and would make a much more boring investment proposition for private equity than a new sort of vehicle which sports claims of revolution, modernity and cleanliness.

Above clip (also posted in this thread of five years ago(!)) has a person controlling an electric multicopter, seeming to have partial success in learning how to control the craft in ground effect hover in 6 minutes, which it looks like is the flight duration that the batteries can provide.
Comparing multiple against a single rotor:

Efficiency.
The generic equations for thrust T and power P are:$$T = \dot{m}\cdot v \tag{1}$$ $$P = ½ \cdot \dot{m} \cdot v^2 \tag{2}$$ with $\dot{m}$ the mass flow of the airstream through the rotor(s) and $v$ its velocity. So for a given amount of thrust, a larger total rotor disk area requires less power. A single rotor covering the outside perimeter of the OP photo would be more efficient than multiple small rotors which leave a large amount of disk space open.

Controllability. The multicopter in the clip has fixed pitch rotors. To control the craft in pitch and roll some of the rotors can be sped up, which tilts the craft and therefore the thrust vector. A simple mechanism if the differential thrust can be supplied rapidly enough, as with current supply to electric motors. Slowing down some of the rotors can always be done rapidly but lowers total thrust, the craft descends while controlling.
The multicopter way of control is simpler than that of the cyclic pitch adjustment of the traditional helicopter. An alternative could be a large rotor without cyclic pitch control, with four small rotors to speed up/down for control.

Translational lift. As a helicopter speeds up, it requires less power to drive the rotor(s) at a given thrust because of the airflow streaming in. As in this answer: the required induced power reduces.
In order to fully profit from translational lift the rotors should be able to adjust their pitch: like in a propeller aeroplane, the angle of attack of a fixed pitch blade reduces as speed increases, ultimately resulting in zero thrust at blade AoA zero. But that requirement negates the simplicity of multiple fixed blade propellers, an arrangement which severely restricts maximum speed.

Noise. Thrust is proportional to tip speed. from expanded impulse theory: $$T = C_T \cdot \rho \cdot A \cdot {(\Omega R)}^2 \tag{3}$$ with ${(\Omega R)}$ being the tip speed. In order to maximise thrust for a given rotor the maximum tip speed should be used: thrust scales with the square value.
The main contributor to helicopter noise is the engine, a turboshaft being very noisy while an electric motor is very silent.

Scalability. Upscaling heavier-than-air aircraft is subject to the square-cube-law. What is relatively easy to do at low weight becomes very problematic at higher weight, and all aircraft focus on weight reduction. A vertical take-off craft even more: thrust must be higher than weight, unlike in a fixed wing aeroplane. Batteries are a major spoiler here since they are heavy.

A possible solution.  Noisy turboshaft and piston engines have very good power-to-weight ratios. Power a multi-copter with a silent piston engine generator, and make the rotors have adjustable collective pitch.

Why are aerial taxis multirotored, instead of a single rotor?

There are not many good technical reasons. Simplicity of control is not an urgent problem to be solved, cyclic pitch technology is mature and has been around for almost a century. The main reason seems to be marketing, because the image of a multicopter automatically associates silent, clean electrical actuation, while that of a helicopter associates with loud engine noise.

There are a few main reasons most electric air taxi concepts have multiple rotors.
1) Mechanical simplicity.  Helicopters are controlled by varying the angle of attack of the blades as the rotate, and the mechanical mechanisms to do this (swashplates) are complex and expensive to build and maintain. The thinking is that with electric motors, you can stabilize the vehicle using differential thrust and eliminate the complexity of those systems.  This has implications for vehicle cost.
2) Noise.  One of the main reasons there aren't any helicopter airlines around now (and there used to be) is that helicopters are very noisy.  Noise in rotorcraft is related to a lot of things, but one of the main drivers is blade tip speed.  With more, smaller rotors, you can have lower blade tip speeds for the same disk area, thereby reducing noise.  Whether this has the potential to reduce noise enough to make a significant difference has yet to be conclusively demonstrated, mostly because there's no clear definition of "enough noise reduction".
3) Safety.  Another argument commonly made for eVTOL air taxis is more motors = more safety, because if one motor fails you have lots of others to keep you in the air.  The validity of this argument depends on how much redundancy you have in the rest of your powertrain, but it principle the opportunity for more redundancy offers a pathway to improved reliability.  There are new failure modes introduced by this multitude of rotors and in general these vehicles have no autorotation capability, making a total power failure much higher consequence; all of which needs to be taken into account.
4) It looks cool There's probably more to this argument than it gets credit for.  Most of the investment and momentum behind the air taxi concept is coming from Silicon Valley and not the traditional aerospace players (who, it must be said, are started to get onboard - especially Airbus). This creates pressure to develop a product that looks and feels revolutionary, to raise the billions required for aircraft development.  Public acceptance of these systems will also be an issue, and public opinion in many large cities is pretty anti-helicopter.
From a performance standpoint the big difference between most multirotor concepts and current helicopters is that lots of multirotor concepts are battery-powered (for noise, local emission, and infrastructure flexibility reasons). Batteries are much worse than avgas from a energy/weight standpoint.  A hybrid-electric multirotor would have broadly similar performance to a hybrid-electric helicopter, assuming they had the same disc loading.

Safety. How do we get redundancy throughout the powertrain, do we have multiple separate battery cells?

The real reason is that the current concept for aerial taxis came from people who don't understand or don't care about aerodynamics. This is one of ten business ideas that Uber is/was pushing for their IPO, and they have had success with the money they put into its marketing. It originated from extrapolation of camera drone technology to human passenger size, but the tech won't scale.
You are absolutely correct that one large rotor is more efficient that many small rotors, but for both hovering as well as lateral motion. Hovering is very inefficient, requiring twice as much energy as a translating takeoff. Small is not necessarily quieter as supersonic airflow at the tips generates noise, and rotors turn at whatever speeds they are designed to turn.
Quadcopters dominate for camera drones as control is simple. Multiple rotors fit small electric motors, which are quieter than small gas motors. Unfortunately, the electricity has to come from very inefficient batteries, or you need a gas electricity generator and are back to noise. Simplicity gets blocked when dealing with failure, so duplicating everything means a quadcopter turns into an octocopter.
Multicopters are an inefficient means to accomplish VTOL, an inefficient flight profile, using batteries, an inefficient energy store. You can expect anything having this configuration to fail.

Perhaps not the main reason, but an important one in addition to the other answers, is IP. The established players in helicopter design & manufacturing are just that, established; they are all firms that have been refining their technology for decades, often with substantial defence funding, so that all of the performance & efficiency gains in their engineering are subject to stridently contested patents. These are worth many, many millions of dollars.
As is often the case with research by these organisations, there will be patents for things they developed that they didn't end up using, that they keep simply to stop anyone else from using. And they will stop anyone from using them for free.
I don't know the status of the patents that cover what started out as novelty toys, which is where these electric-powered, microprocessor-controlled & stabilised multicopters have developed from - presumably they are not held by Boeing, Lockheed, Bell, Sikorsky, Agusta, et al.
The history of aviation is littered with advances that have happened simply as a result of avoiding patent infringement, however. For example, the Wright Brothers were consumed with stopping anyone else, particularly Curtis, from using any of their ideas. They spent as much effort in litigation as they did in building & flying. Rolls Royce & GE are in a constant dance of patent infringement with their engines to this day, as are Boeing & Airbus. They really hate having to licence technology from or to their competitors.

The concept drawing in the original post looks like it is intended to compete with Robinson Helicopters.  Robinson uses Lycoming and Rolls Royce engines.

The concept drawing shows a safety advantage of the multiple rotor design:  You can see the beams that support the multiple rotors.  The beams are beneath the rotors.  This makes it less likely that passengers will accidentally put themselves in the way of the rotor(s).
From the point of view of the concept artist, it is much easier to make the beams that support multiple rotors look both solid and circular than it is to make a single rotor look solid and circular.


text:
Does it exist? Environmentally-friendly/safe fluorescent liquid to make sea crashes easier to find?
Has this been tried in aviation history?
To make airplane sea crashes easier to find, can we use a colored liquid that is lighter than water, environmentally-friendly and safe, with fluorescent properties so that if an airplane crashes into the ocean, this liquid would leak out and float to the surface. During the day, the color is noticeable by satellite and by night it glows.
Does something like this exist? Can it be easily implemented? Has it already been attempted?

Rough approximation:   How many gallons of this stuff would you need for it to not dissipate in minutes?  How much would that weigh?  How often to airplanes crash in the sea?   The cost and complexity just doesn't even come close to the benefit.

Good points. Those are questions that I was looking for to see if anyone has already tried it. I'm thinking in light of the Malaysia flight.

For spacecraft splashdowns (certainly Gemini, maybe others) they used a green marker dye, but I don't know how long it lasted.  That would be a good thing to start with as they must have tested how long the traces were visible when choosing it.

http://prestodye.com/sea-dye-markers/ says "30 to 40 minutes", depending on sea conditions. Apparently there's a standard: MIL-S-17980D.

Exactly what I was looking for. Do you have a link? Thanks @Andy !

Thanks for the link @RogerLipscombe, I wonder if they can make it last longer...

You may edit your question to reflect your previous research and why you ask this question here.

For spacecraft splashdowns, the recovery teams know where it is within a very small area.  For lost aircraft, the area is huge.  To spot the die, you would need a geostationary satellite or, redeploy a military one.  You can't do that in time before the die has dissipated and, or, been spread by the currents.  I really can't see any benefits to marking a crash site with die.

Thanks to those who commented and provided answer-worthy comments. Thanks!
What is already in existance today:
@Andy commented:

For spacecraft splashdowns (certainly Gemini, maybe others) they used
  a green marker dye, but I don't know how long it lasted. That would be
  a good thing to start with as they must have tested how long the
  traces were visible when choosing it.

@RogerLipscombe commented:

prestodye.com/sea-dye-markers says "30 to 40 minutes", depending on
  sea conditions. Apparently there's a standard: MIL-S-17980D.

And for the challenges:
@abelenky commented:

Rough approximation: How many gallons of this stuff would you need for
  it to not dissipate in minutes? How much would that weigh? How often
  to airplanes crash in the sea? The cost and complexity just doesn't
  even come close to the benefit.


text:
What are the meanings of these terms used in ATC ground communications?
Regarding ATC ground communications, what/who are the following callees? Are these aircraft, or vehicles, or people?

[Airline name] maintenance
[Airline name] tug
[Airline name] mechanic

Also related : https://aviation.stackexchange.com/q/29706/679

Thanks, these do answer for the first half of my question. But the second half still remains.

Please avoid asking multiple questions in one if possible. Since the first half of your question is already answered elsewhere, it might be best to remove that part completely and focus on the second part.

Sorry, I edited the question.

This is the closest I've got as for an answer. This information was gathered from a comment came in for an answer which is now deleted together with the answer itself.
This answer needs improvements and confirmation from someone who is more knowledgeable.
1. [Airline name] maintenance
An aircraft manned by a mechanic on the ground. Usually calls for repositioning.
2. [Airline name] tug
A tug works for or operated by the named airline.
3. [Airline name] mechanic
A possible synonym for [Airline name] maintenance

If you are driving a vehicle anywhere within the movement controlled area of an airport you need to be in contact with the ground controller.
1 & 3 are virtually synonymous, it is a person, a mechanic, working for the named airline's maintenance department, driving a vehicle.
2 is a person driving a aircraft tug vehicle.

I think it's not the case. From a comment came in for an answer (now deleted) said ATC won't call to people but vehicles or aircraft. And also suggested,

An aircraft manned by a mechanic on the ground. Usually calls for repositioning.
A tug serves or operated by a particular airline
As you said a synonym for the first one.

@Nipuna, I did not use the term pedestrians, I specified people in vehicles.  (in case that is causing any confusion)  Good point about a mechanic, or other maintenance personnel repositioning an aircraft.  But, it seems you have enough information to clear things up, right?  If you don't like my answer you can always provide your own.  I don't feel compelled to add more detail because it isn't that complicated.

Hey Michael, I meant nothing offensive. I was just confused earlier.

I'd imagine it's possible that #2 is not just the tug vehicle, but also a tug with an aircraft attached (such as if the aircraft is being moved from/to a maintenance facility or other non-pushback moves).


text:
Why does an airplane require 3 pilots on board?
A car requires only 1 single driver. Why do airplanes require 3 pilots given that each pilot does not come cheap to the airline? Furthermore, a plane can go on auto-pilot while a car cannot. Could there be more room for efficiency by reducing the number of pilots needed?

Is your question restricted to airliners?

Which airplanes require 3 pilots? The vast majority of airlines only require 2 (e.g. 737, A320).

Actually, for all but very long haul flights, airline aircraft only require two pilots, a Captain and a First Officer. For those long haul flights that exceed the duty time in a pilot seat, a relief pilot is also carried.
Older aircraft often also had a flight engineer. Technically speaking the f.e. wasn't usually required to be a pilot, but he was a very necessary crew member. You could say that airlines became more efficient crew-wise when they moved from 3-man cockpit crews to 2-man cockpit crews. For example, the 747-100/200 series uses 3-man crews, but the 747-400 uses 2-man crews. The change was made possible by using automation and instrumentation that wasn't available when the first 747 models came out. Indirectly the increase in engine reliability also helped. If you lost an engine in an 3-man crew 747, the typical manner of handling the loss was to have the first officer fly the airplane while the captain and the f.e. worked the problem.
To illustrate the increase in automation, the 747-100/200 series had, typically, seven or nine fuel tanks, and there was a fuel burn schedule that had to be followed to keep the structural stresses and balances between different levels of the tanks within limits. The f.e. took care of that, doing it manually by throwing switches on his panel. The 747-400 and follow on models do that automatically by computer.
Basically the number in the cockpit crew is determined by safety. There's the basic consideration that if you had only one pilot, and that pilot died or otherwise was disabled, that might well be catastrophic. Beyond that, though, there's the matter of what all has to be done and for how long. Pilots make mistakes, and the longer they've on duty, the more mistakes they make. And if an emergency occurs, the work load can get very high.
You can't reasonably compare an aircraft to a car for at least two reasons. First, a car is moving in only two dimensions, an aircraft in three. Second, a car can stop moving, an aircraft can't; it has to keep moving. Let's say your car loses power. Usually that won't result in anything more than inconvenience. If your aircraft loses power, you've got a much more serious problem. Most airline aircraft have at least two engines. Losing one isn't going cause a crash in most two engine aircraft, losing all power will.

Would you happen to know if trains also have 2 or more drivers given the safety concerns and the number of passengers that they are carrying?

@user1824987 Bear in mind that, in most cases, if something is going wrong, a train can just stop and wait for somebody else to show up and help solve the problem.  Planes don't have that option.

@user Trains tend to have a dead man's switch that automatically stops them if the driver is incapacitated. Also, long-distance trains have a conductor/guard, and there is an emergency brake that can be triggered from the cars.

Furthermore, some countries require long-distance bus drivers to have relief drivers.

Trains also often have emergency stop buttons in the passenger compartment. Planes, for obvious reasons, do not.

In a car, you can choose to either drive or work the problem. That's not an option you have in an aircraft. You need to keep flying while working the problem, the flying part made more difficult by the problem.

Most of the commercial airlines now require only two pilots- a captain and a first officer. It is in a large part, regulatory (GA and combat aircraft have only a single pilot). It is perfectly possible to fly a transport aircraft with a single pilot.
In fact, there have been calls for eliminating the second pilot. There are some points though.

The roles of the captain and first officer are complementary, not identical; though it is perfectly possible to have only a single pilot, having two helps.
One important reason is safety/redundancy- If something happens to a pilot en route, the other one can take over and land safely. this safety by redundancy extends to all aircraft systems.
In long haul flights, two (or more, usually) pilots are required (both practically and by regulation).
Another point is that autolanding is not possible in all the airports. it needs the necessary ILS.
One problem with comparing aircraft with cars (or other surface vehicles, like trains) is that the effects of losing control and power in these cases is completely different. A car can simply go hit something and stop- that is not an option with an aircraft; it'll fall. Trains usually have a dead man's switch that'll apply emergency brakes if the pilot's presence is not felt.

In a land vehicle most of the time if something goes wrong, either mechanically with the vehicle or medically with the driver you can just stop. Stopping may be inconviniant but it's unlikely to be deadly.
An airplane on the other hand is a complex machine (and the bigger they get generally the more complex they get) and if something goes wrong requires careful management to get it safely back on the ground.
Autopilots can be helpful in some phases of flight but they still require manual input and landing on autopilot requires ground infrastructure that not every airport has.
For light planes with small numbers of passengers (or no passengers at all) the risk of having a single pilot is deemed tolerable. On the other hand having an airliner crash because one person was incapacitated is not considered acceptable.
So the flight crew on larger planes is one larger than is strictly needed to fly, navigate and land the plane. Older planes had three flight crew (two pilots and a flight engineer), more recent airliners have added more automation and got rid of the flight engineer.

Airlines sometimes elect to fly planes with more pilots than is actually needed.
On reason for that is training.
Any time spent in the cockpit is increasing the pilot hours rating, even if only seated in the jump seat, without access to controls.
On a side note, adding an other pilot might also be helpful in case of an emergency; this was considered as a contributing factor in the relative success of the UA232 crash for exemple.


text:
What material is used to make the hot sections of jet engines?
What metal alloy is used for the hot section of a jet engine? Specifically the exhaust nozzle? I have found mention of a titanium alloy and nickel alloy but nothing with that much detail. What sort of metals does one have to use to create something that can withstand temperatures of 650 degrees Celsius? Thanks

To be fair, the metals are at roughly 90% of their melting point temperature. If they would get any hotter then what they actually get, they would start melting. What is more amazing is that in spite of them being pushed so hard they still have such a great lifetime.

Short answer

Fan: Aluminum, titanium, or stainless steel

Compressor: Nickel-, cobalt-, or iron-based alloys. Additive are aluminum and/or titanium, chromium, as well as rare earth elements like yttrium.

Combustion chamber: Superalloys with refractory metals such as tungsten, molybdenum, niobium, tantalum. Ceramics and ceramic-metal mixes.

Turbine: Nickel-based superalloy, outside air is circulated through channels inside of the turbine blades. For lower pressure turbine blades iron-based superalloy or even stainless steel. The metals used for turbine blades are often grown as a single crystal.

Exhaust nozzle: Nickel Inconel and stainless steel alloys.

Casing: Aluminum or polymer matrix materials.

The high-pressure turbine is, with the combustion chamber, very hot (more than the exhaust nozzle). You may read this Wikipedia article which has a short list of materials used for turbine blades (with alloys names and cooling techniques).

The fan pushes about one ton of cold air in the engine every second in high power turbofans. This is why temperatures and pressures can be so large after compression and after combustion.
All quotes are from Nasa Guide To Engines, 2007.

In 1903, the Wright brothers built an aluminum
block engine because of its light weight compared to cast iron. Its
melting point of 660 °C was well above the engine’s operating
temperature, so for them it was a good choice. However, aluminum could
not be used in the hotter parts of a turbine engine where temperatures
reach of 1800 °C or more because it would melt.

Fan

This typically does
not get very hot (<150 °C) so aluminum, titanium, or stainless steel
are all suitable for the fan blades. Most engines use titanium because
it has a high strength-to-weight ratio, is corrosion and fatigue
resistant, and would be able to withstand the impact of a bird strike.

Fan example (with a fan blade missing after the engine blew apart).
Compressor section

The pressure of the air can be raised up to 30 times and the
temperature, depending on the number of stages in the compressor, can
rise to 1000 °C. Here the materials must have high strength at high
temperatures; must resist fatigue, cracking, and oxidation; and also
must resist “creep.” Creep is the tendency of a material to slowly
change shape when stressed at high temperature. Since no single metal
would have all the desired properties, an alloy (a mixture of metals)
is used. Very high- temperature alloys are called superalloys and are
generally nickel-, cobalt-, or iron-based alloys. Aluminum and/or
titanium are added for strength, and chromium, as well as rare earth
elements like yttrium, are added to improve corrosion resistance.

Compressor example (high pressure rotors)
Combustion chamber

Temperatures can exceed 1800 °C and again superalloys are used, but
without the titanium or aluminum for strength because there are no
moving parts. Instead, refractory metals are often added to a
superalloy. These are metals of unusually high resistance to heat,
corrosion, and wear such as tungsten, molybdenum, niobium, tantalum,
and rhenium. They are used in alloys and not as pure metals because
they are among the densest of all the elements, a negative property
when it comes to aircraft that need to keep weight to a minimum.
Ceramics and ceramic-metal mixes are also used here because of their
high heat resistance. We are familiar with pottery, tile, crucibles,
and fire bricks as types of ceramics. They have very high melting
points and don’t require the cooling systems like those needed to keep
metals from melting so they make for lighter, less complicated engine
parts. The down side is that they tend to fracture under stress, so
engineers seek to create new ceramics composites that incorporate
other materials to improve properties.

Combustion chamber example
Turbine

High-pressure turbine blade (source: Wikipedia)

The first set of turbine blades are in the highest pressure, hottest
part of the gas flow and are generally made of nickel-based superalloy
or ceramic blades. Unheated outside air is circulated through channels
inside of the turbine blades to keep them from melting in this extreme
environment. Further down the engine lower pressure turbine blades
often sit. Since the gases have somewhat cooled by this point, the
blades can be made of iron-based superalloy or even stainless steel.
It is interesting to note that for strength, the metals used for
turbine blades are often grown as a single crystal. A close look at
most metals and alloys show that they are composed of crystals (also
called “grains”), and the places where the crystals meet are called
grain boundaries. A material is weaker at the grain boundaries than
within the grains—especially at high temperatures— so turbine blades
fashioned from metal formed as a single grain (no boundaries) are
stronger.

See single crystal material (known as monocrystalline material in electronics) .
Turbine example (high pressure stator)
Exhaust

Exhaust from Boeing 787 engine (GEnx, one of the world's largest jet engine - Source)
From FAA Aviation Maintenance Technician Handbook - FAA-8083-30:

Inconel and stainless steel alloys. The Inconel [nickel-chromium-iron]
alloys are frequently used in turbine engines because of their ability
to maintain their strength and corrosion resistance under extremely
high temperature conditions.

See Inconel details.
Casing

Although it need not withstand high temperatures like the core of the
turbine, the materials here need to be strong enough that if a blade
were to break off it would be contained within the casing and not
enter the wing or cabin of the aircraft and cause further damage.
Aluminum or some polymer matrix materials are used as engine casings.

I would like to say this is one of the best answers I have read in quite a long time. Thank you for making it so clear

Some of the newest GE engines use carbon fiber fan blades.

First, the hot section is not the nozzle, but the combustor and the high-pressure turbine.
Second, 650°C is nothing for modern high-temperature alloys like Inconel. The top gas temperature in a modern jet turbine is more like 1500°C, and the turbine blades tolerate temperatures of around 1200°C. For military turbines and the temperature in the combustor, add a few hundred degrees on top of that. Film cooling allows to run high-performance turbines at a few hundred centigrades below the gas temperature. Steel would melt and other materials like titanium would quickly oxidize, and only nickel alloys or ceramics are up to the job. Being still too brittle for everyday use, ceramics have not managed to escape the laboratory, so nickel alloys is all we have for now.
A popular choice for gas turbines is Inconel 792.

An interesting presentation listed on SlideShare shows material strength as a function of temperature. The presentations are not listed as freely available under Wiki commons, so I've digitised them.

Specific strength as a function of temperature, no units. Nickel alloy is the strongest only at high temperatures.
Then another slide show lists the materials as:

Fan: titanium alloy
Low Pressure Compressor: titanium alloy
Intermediate Pressure Compressor: titanium alloy
High Pressure Compressor: nickel alloy
Combustor: partially Yttria stabilised zirconia, with a melting temperature between 2,700 and 2,850 °C
HP Turbine: single crystal nickel alloy, coated in ceramics
LP turbine: single crystal nickel alloy
Exhaust: single crystal nickel alloy.

The turbine blades are grown as a single crystal, and are mounted in an environment that is 400 deg hotter than the melting point of the blade. It is cooled with air from the compressor.

HP Turbine: single crystal nickel alloy, coated in ceramics and cooled with compressor discharge air (unless small gas turbines are considered)


text:
When do pilots disconnect the autopilot on an ILS approach?
In clear weather, when do pilots disconnect the autopilot, if the plane is flying an ILS approach and the autopilot is in "approach" mode (tracking both localizer and glideslope)?
Would the answer differ significantly in different planes, for example Boeing 777 vs Airbus A320?

That's pretty much up to the pilot. Latest at autopilot minimum disconnect height (usually around 50ft), earliest any time below RVSM airspace. The company SOP or airport local regulations might also restrict.

I don't agree this question is "opinion based". It has a valid answer, it just happens that the OP does not know the answer is "up to the pilot".

Asking "when is it BEST to disconnect..." would be opinion based. Asking when pilots DO disconnect is a question about hard, verifiable, objective FACTS.  The question as posted is entirely the latter and is not in any way asking for opinions. The fact that the objective answer is, pilots have the latitude (within stated limits) to disconnect as he thinks best, doesn't make the question or answer now one of opinion.

Also, A/P in RVSM airspace applies to level flight, not climbs or descents.  Hand flying the descent from FL 410, while perhaps a little pointless, is entirely legal.

In clear weather, I would rather hand-fly the ILS approach.

Why do pilots disconnect the autopilot at all on an ILS approach before they slow to taxi speed and pull off the runway?  The autopilot can land the plane better than the squishy pilot can.

The decision to disconnect the autopilot is made by the pilot and can be made at any point as long as the operational limitations of the aircraft are satisfied (according to the type of ILS). The pilot also has to satisfy the applicable regulations and company SOPs (as @Sami already pointed out). Note that this depends on the pilot decision too- the pilot can fly the missed approach in autopilot if he decides so.
Usually, the aircrafts have minimum altitudes below which the autopilot has to be disconnected, which are given in the aircraft operating limitaions. For example, for Airbus A340,

CATEGORY II
If the crew performs an automatic approach without autoland, the autopilot must be disengaged no later than at 80 feet.

For Boeing 777:

Autopilot/Flight Director System
The autopilot must be disengaged before the airplane descends more than 50 feet below the MDA unless it is coupled to an ILS glideslope and localizer or in the go–around mode.
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 200 feet AGL.

For Boeing 787:

Autopilot/Flight Director System
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 100 feet AGL.

As an example in GA aircraft, for Cessna C172 G1000:

The autopilot must be disengaged below 200 feet AGL during approach operations..

As you can see, there is not much difference.

on the Boeing AP what are LAND 2 and LAND 3? Is that full autoland?

@TomMcW  excellent question -- created here: http://aviation.stackexchange.com/q/24119/7532

Should probably mention that for category III ILS approaches, the autopilot must never be disconnected before the aircraft pulls off the runway, or else a go-around is required.

I am a B777 pilot; on approach I typically disconnect the Autopilot once visual contact is assured and I am inside the Final Approach fix.
If there is any chance of a possible missed approach, (especially with a complicated missed approach procedure) I will leave the AP on until there is virtually no chance of a missed approach due to weather or other conflicting aircraft on the runway or elsewhere.
Most of the pilots I fly with tend to do the same.
On departure, we generally hand fly until about 10,000' to keep up our skills. If the departure procedure is complicated, we will ask for the AP on at 200' so there is no chance of messing up the departure procedure.

I'm really glad to hear that at least some pilots are still hand flying. I retired in 1999. I realize that my way of doing things and the equipment I was using are both outmoded. However, I cannot the escape the feeling that our way of doing things back then was better, if only because hand flying is a helluva lot more fun than watching the autopilot. Most of us hand flew to the first cruise altitude, from the top of descent, and rarely used the autopilot for an approach. The era of the ops specs requiring such (if they do) had not yet arrived.

In calm wind or under 5 knots on a cat 3 then ride that sucker all the way down and it will disengage when the rear wheels hit the runs way, but keep your thumb on the elevator trim in case it doesn't.  In most normal conditions keep it around 50 ft. agl.  In low visibility then keep it on until you see the runway lights and feel safe to disengage and land/glide manually.  If you start to oscillate before touchdown then turn the A/T off reduce to idle and disengage the Auto Pilot and dip your right rear or left (depending on wind direction) and grab that runway letting the plane settle.  If you are cat 2 then disengage no lower than 20 feet agl, so you can adjust your glide and attitude or roll for a softer landing.  If you are cat 1 then approximately 50 feet or until you see the lights on the runway in low visibility. Discretion is key here or course, but trust the glideslope in low visibility as long as possible and make sure you have the correct QNH and be ready to mash that TOGA button if something isn't right.


text:
Just got a quadcopter, and not sure about a piece that came with it
My apologies if this is the wrong forum, but I have seen hot questions about drones/quad-copters from here in the past.
I received a quadcopter recently (X5C Explorers), and it has a piece I can not seem to identify online or in the packaging/manual itself.  It is orange, and appears to have a USB port on one end and an slot for possibly an SD card on the other (not too sure to be honest, but the quadcopter has a camera so probably has something to do with that).  Picture included below.  So any idea what this thing is and more importantly, how it should be used?
.

This question does not belong in this SE, however this cable is for uploading pictures from the SD Card (Supposedly from your drone camera) to your computer via USB. You just plug the SD Card in the end it belongs in and plug it into a USB port on your computer.

Ahh that makes sense.  It just didn't look like something that would plug directly into a computer at first (feels very light), but I suppose that is exactly what it is for.


text:
what type of sensors does the Boeing 737 MAX use for MCAS?
I can imagine there are several different ways to measure angle of attack (accelerometers, relative pressure measurements between pitot tubes, etc), but I'm curious which sensors the 737 MAX uses for its MCAS system since it's been in the news recently.

See related question: https://aviation.stackexchange.com/questions/61011/how-many-aoa-sensors-does-the-737-max-have

Faulty ones, apparently.

The pitot tube has nothing to do with the angle of attack. It is used for measuring pressure which in turn gives you the airspeed.
Accelerometers are used for the Inertial Navigation System.
The angle of attack is another sensor (shown below): the principle is that it rotates and reads the angle between the current position and the reference position.

Regarding the 737 MAX, there are two AoA sensors one on the captain side and one on the first officer side.
The MCAS reads the AoA from the captain side.

appreciate the info! Just to not seem like an idiot, there have been studies as far back as 1955 showing that pitot tubes could be used for AoA measurement: https://apps.dtic.mil/dtic/tr/fulltext/u2/102442.pdf

That's interesting! I wasn't aware of it

The IRS can compute the flight path vector which, knowing the airspeed and ground-speed and thus wind speed could actually be used to calculate a pretty good estimation for the angle of attack. It is probably not fast enough through.

@Jan It would not be very accurate, as the vertical motion of the air is an unknown, and the variation of vertical airmass speed seen in normal weather conditions is comparable to the range of the vertical component of the incident airflow at typical airspeeds and AofA. No doubt one could have a more sophisticated model that included the airplane's response to both gusts and control inputs, and so attempt to estimate the vertical motion of the air by the aircraft's response to it, but there is little point in doing so, as the value can much more easily be directly measured.

@NicolasHolthaus That is an interesting paper, but note that the pitot tubes described here are not simple ones like those used for airspeed measurements - they involve multiple ports, each with its own sensor, arranged around a conical or hemispherical body. Some of the other ideas here are quite wild, such as optically tracking smoke.

@sdenham good point, you could try and measure the vertical speed, too, but that is even slower :D The aoa vanes are already pretty good, no need to change a running system. (if you install and use multiple sensors of course)

I think you are talking about the heavy MCAS "corrections" that led to the two crashes.  The MCAS is part of the STS (Speed Trim System). Apart from the Angle of Attack sensor, MCAS also checks that the flaps are up (retracted) and the auto pilot is off before it triggers the heavy nose-down trim.  Some sources add that MCAS also needs a high bank angle and the engine at high power before it activates.
BTW the MCAS does not check to see if the AoA sensor readings make sense.  It accepts the sensor readings blindly.


text:
Is there a name for change in attitude with respect to time?
I'm in the process of writing a flight-dynamics software program, but I'm not sure what to call the derivatives of the aircraft attitude. If it was in one dimension, they would be the "angular velocity" and "angular acceleration" respectively.
In aviation, is there a special name for these vectors?

I love a programmer who's serious about naming his symbols. Thank you :)

@Steve you're welcome. IMHO it's the most important part of the whole business.

In general 3d physics contexts, "angular velocity" is typically understood to be a 3-vector. I think what you have in mind would better be understood as "magnitude of angular velocity". (In one dimension, I'm not sure how to define rotation ;) but I think I understand what you mean.)

@Praxeolitic Angular speed?

@immibis That phrasing would feel unusual to me but the intent would be obvious. I don't know if I'm in the minority there.

To be pedantic, they aren't vectors.

The components of attitude vector are called:

yaw (or heading) is the angle of longitudinal (x) axis in horizontal plane,
pitch is angle of longitudinal (x) axis from the horizontal and
roll is angle of lateral (y) axis from the intersection of the yz (orthogonal to longitudinal axis) plane with horizontal.

And their derivatives are usually yaw-rate, pitch-rate and roll-rate. Second derivative names probably vary.
Regarding coordinate system, the first axis, called x, is always longitudinal and positive direction is forward. The second axis, called y, is usually lateral one, but positive direction is right in some systems and left in others. And z completes a right-handed coordinate system (so your vector products work the usual way), so z down if y points right.
Edit: I thought u,v,w is sometimes used as alias for the axis, but actually they are usually rather used for the velocity vector components.

so extrapolating from this, attitude-rate would be a plausible name for a vector consisting of the changes in yaw, pitch, and roll?

@NicolasHolthaus, yes, you could call it that.

I've never heard it called that, but it would make sense. The closest I've seen is "Rate of attitude change" or "Rate of change of attitude" - or specific to each eg "Yaw rate", "Rate of change of pitch", "Roll rate" etc. They tend not to be combined into "attitude rate", but I don't see why they couldn't be - semantically it makes sense.

"Pitch rate", "roll rate" and "yaw rate" all seem logical for their derivatives.

@StephenS -- for a different viewpoint see https://aviation.stackexchange.com/a/98197/34686

I know this is an old question, but I wanted to throw quaternions (and quaternion rates) and other non-Euler angle attitude (and rate) representations into the mix.
While yaw, pitch, and roll are frequently used for aircraft, quaternions are also used for aircraft and inertial guidance systems. Other attitude representations include principle rotation vectors, direction cosine matrices, classical Rodriguez parameters, and modified Rodriguez parameters. There are also a lot of other Euler angle representations available. All have their pros and cons including existence and type of singularities in the equations.
Hanspeter Schaub (my current graduate advisor) has a coursera course with a lot more information if you're interested.
https://www.coursera.org/lecture/spacecraft-dynamics-kinematics/4-euler-parameter-quaternion-definition-tOeps

I believe you are looking for yaw, pitch and roll:

Pitching for the nose moving up and down.
Yawing for the nose moving side to side.
Rolling for the wings rocking back and forth.

I'm familiar with the components of attitude, which are pitch, roll, and yaw. What I was looking for was what to call the change in pitch/roll/yaw with respect to time, when all three quantities are grouped into a single vector.

It's important to recognize that

while "roll rate" is the rate of rotation about the roll axis which is the rate of change of the bank angle

the "pitch rate" is the rate of rotation about the pitch axis which is often not the rate of change of the pitch attitude

and

the "yaw rate" is the rate of rotation about the yaw axis which is often not the rate of change of the yaw attitude, i.e. the rate of change of the heading.

If this is unclear, consider what happens if the aircraft rotates about the pitch or yaw axes at bank angles near 90 degrees.
Therefore the terms you are looking for appear to be the "rate of change of the pitch attitude", "rate of change of the heading", and "roll rate", for the rate of change of the pitch, yaw, and roll attitudes respectively.
The "rate of change of the heading" could sometimes be called the "turn rate" as well, but strictly speaking this would usually only be the case if the sideslip angle (and the angle-of-attack) were constant, not changing.2  The "turn rate" is the rate of change of the direction of the horizontal component of the  flight path.
Footnotes:

Link to an ASE answer using the phrase "yaw angle" to mean heading: What are the exact meanings of roll, pitch and yaw?

Or in cases where the sideslip angle and the angle-of-attack are changing in a synchronized way such that the rate of change of heading is (at least momentarily) exactly equal to the rate of change of the horizontal component of the flight path.

authors: Павел Панюшкин


text:
Is AA actually flying the 737 MAX?
In flightradar24 I only see 737 MAX flying from Gol Airlines and Aeromexico, but none from AA.
Is American actually flying the 737 MAX or is FlightRadar24 reporting aircraft types wrong ?
I also see a few MAXes with a Boeing ticker flying in the Seattle area, probably delivery tests.

According to their website, they will start commercial flights using the 737 MAX on 29 December, but will be testing their aircraft on non-commercial flights before than:

We’ll begin with non-commercial flights in early December 2020 before the official return of the 737 MAX. On December 29, we’ll resume scheduled service with 2 flights a day (1 round trip) through January 4, 2021, from Miami (MIA) to New York LaGuardia (LGA). We expect to phase more of the aircraft into our schedule through January, with up to 36 departures from Miami.

(aa.com, emphasis mine)


text:
Why fly VFR at all?
Really novice question here: if both the pilot and the aircraft are instrument-rated, why would anyone fly VFR? IFR lets one fly in a wider range of weather conditions and at night while there are no situations where VFR is allowed and IFR isn't. Or are there?

Sightseeing is a little hard to do when you are flying an IFR flight plan.

I've read a few articles where an ATC was sending an IFR pilot way out of their way so they cancelled IFR and finished their route VFR to save time

IFR is a lot more work. It would be like taking a hike in the wilderness while looking at your phone; oh wait, people do that...

Many years ago, I got to listen to an advanced instructor teaching an advanced student about "special VFR".  One thing he said stayed with me.  On a special VFR clearance, you can fly out UNDER the clouds and weather.  If you file IFR, ATC is more than likely going to put you IN the clouds and the weather.

http://www.flyingmag.com/flying-vfr-offers-greater-freedom-and-flexibility

@RonBeyer I suppose you could just file GPS Direct through a bunch of waypoints that make a circle around the sights you want to see. ATC will probably "fix" that for you though.

@voretaq7 "Cleared Direct KDEST"... Show's over guys! :)

(This answer is based on light aircraft in the US.)
Leaving aside any scenarios where you must file IFR (class A, IMC) and any where you can't (pilot and/or aircraft not IFR-capable), it comes down to whether the 'overhead' and benefits of operating IFR are worth it for your particular flight. By the way, your question seems to assume that IFR is required at night, but night VFR is legal in many countries.
The 'overhead' of operating IFR is firstly in planning: there are different rules for fuel reserves, altitudes, airspace, alternate airports, weather minimums etc. Generally speaking you need more time and thought to prepare and file an IFR flight plan. Secondly, operating IFR potentially places a lot of restrictions on you: ATC can delay your takeoff, give you vectors that take you miles out of your direct route, put you in a hold, require position reports, and generally keep you busy. As a pilot, you have to perform at a 'higher' - or at least different - level.
For many people, that's already reason enough to file VFR if conditions allow (don't forget that in the US there's no need to talk to ATC at all on many flights). But the purpose of the flight is important too: IFR more or less assumes that you're flying from A to B on a fairly direct route. If you're training, or sightseeing, or dropping parachutists, or just flying around for the fun of it then IFR isn't really appropriate or useful. You can just get flight following instead, which gives you the benefits of ATC keeping an eye on you, without any of the IFR rules to follow.
And regarding your comment about IFR letting you fly in more weather conditions, there's a pilots' saying in the southern US (and probably many other places) that "if the weather's good, file IFR; if it's bad, file VFR". The reason is that Florida and other southern states get a lot of convective activity and it's very common to have to pick your way between thunderstorms and building cumulus towers to get where you're going, or just for a more comfortable ride. By remaining in visual conditions you're able to see what's going on with the clouds and being VFR means you're more or less free to change course and altitude as needed to avoid them. If you're IFR, ATC may put you in a cloud layer where you can't see anything and vector you closer to the buildups than you'd like. VFR just gives you a lot more options in general.
Finally, are there any scenarios where only VFR is allowed, even for IFR-capable flights? This might be different in different countries, but offhand I can't think of any in the US. IFR minimum altitudes are higher than VFR ones, so you can't fly IFR at 500' AGL, but I guess that's not really what you're thinking about. Maybe someone else will come up with something.

Some airports have no IFR landing, for instance.

@yo'  ATC can clear you for a visual approach when you're on an IFR flightplan. You have to be VMC at that point, but the IFR flightplan gives you all its benefits up to that point, such as descending through an overcast deck down to the MEA, then report "field in sight" and get cleared for the visual approach from there.

Having an IFR flight plan to an airport with no instrument approach can be a luxury in some countries, because it depends on (a) GPS navigation onboard the aircraft, or (b) suitable radio equipment (at least an NDB) in the close proximity of the airport. E.g. many islands in the pacific are served by small planes in the local area, and some of them are not even covered by ATC.

Also, in much of the western US at least, if the weather is bad enough to require flying IFR, I'm not going to go flying.

There are plenty of mountainous areas where the minimum IFR altitude is unreachably high for a normally-aspriated aircraft without oxygen.

There are a few places in the US where only VFR flight is allowed. There are several VFR corridors through the Class B airspace around Los Angeles. There are several sightseeing routes through the Grand Canyon that, if my memory is correct, are VFR only. There is also a VFR corridor for sightseeing up the Hudson River in New York. But mostly, if you can fly it VFR you can fly it IFR.

VFR is the basics of flight. In VFR, you learn takeoffs, landings, turns, stalls etc., with plenty to visibility to help you recover should things go wrong.
IFR flight puts more workload on the pilot.
You won't want to fly aerobatics in IMC.
IFR requires instruments. Instruments can fail.
IFR requires more planning. You have to choose a route, tune VOR stations, join airways etc.
Not all places have navigation radios on the ground. Many small airports don't have anything more than a grass strip and a few houses beside it.
Sometimes you don't want to stay on predefined routes, for example in a search and rescue mission.

It is true that most commercial operations today are carried in IFR. However there are still plenty of other flights, such as private flights to a cousin's house, sight seeing tours, aerial photography, banner towing, gliding, parachuting, crop dusting, search and rescue etc., that are conducted in good visibility and require the pilots to navigate using visual references.

Add cropdusting to that list...

For me, and I imagine for most recreational pilots, a good many flights are not between two designated airports, let alone two airports with instrument facilities.  Say I'm heading out for an afternoon at the hot springs by the Black Rock, where the 'airport' is a bit of dry lake.  Maybe I decide to visit my landsailing friends who're camping at Blue Wing (another dry lake).  How do I do that, flying IFR?

Nice answer, although I'm not sure exactly what you mean with #6? You can file IFR to a grass strip with no instrument approaches if you want, at least in the US.

@Pondlife You must file IFR/VFR and change to VFR in Europe. The AIP lists which airports are VFR and which IFR/VFR. (Are there any IFR only?)

@VladimirF -- I suspect Heathrow is....

"IFR flight puts more workload on the pilot." Nope.

@user IFR flight puts more workload on the pilot: It can, depending on the nature and circumstances of the flight in question. A given IFR flight will typically require greater pilot workload compared with a given VFR flight; the minimum workload required is generally greater. It is certainly a legitimate reason why pilots choose to not fly IFR.

That is so completely not true. Flying VFR I am responsible for my navigation and keeping out of areas i shouldn't be in. Flying IFR I am told what to do by someone else. Indeed, the planning face might be more thorough but it sure isn't flying IFR.

IFR would not be feasible for a lot of different types of recreational and professional flight activities.
For a majority of the flying that I used to do at one of my old jobs, I would not have been unable to get an IFR clearance had I wanted to. That notwithstanding, the routing would have been so complicated that it would have increased my workload—not to mention the controller's workload—to the extent that IFR would not have been feasible.
Many types of mountain flying would simply be impossible to do under IFR. The same goes for most ground proximity flying.
While not necessarily recommended, a pilot could fly VFR into an active MOA, whereas an IFR flight would not be cleared into that active MOA.
Regarding weather conditions, the fact is that I could legally fly in worse weather than would be allowable for many IFR operations, though to do so would—in some cases—be against company rules. It simply is not true that there are no situations in which IFR would be allowable where VFR would not.

authors: Vladimir F Героям слава


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How long will an aircraft need to fly before it can land without dumping fuel?
Now, I know perfectly well that the literal and unhelpful answer to the question is long enough to burn sufficient fuel that it is no longer overweight for landing. What I'd like to understand is whether it is possible or not to give an answer about what's typical.
I am surprised that after flying all the way from Moscow to Ireland this aircraft had enough fuel on board to be still overweight (even given that it still had to go all the way to the Dominican Republic):

An Azur Air Boeing 767-300, registration VP-BUX performing flight ZF-973 from Moscow Vnukovo (Russia) to La Romana (Dominican Republic), was enroute at FL320 about 90nm south of Shannon (Ireland) when the crew decided to divert to Shannon reporting all their lavatories were blocked. The aircraft dumped fuel and landed safely on Shannon's runway 24 about 90 minutes later.

Typically, how much of an airliner's flight will be in an overweight-for-landing condition?
Does it vary so much between aircraft types, distances, passenger/cargo weights and other conditions that it's not simply possible to say what is typical, or is it possible to say that the case above is (for example) unusual?

It depends on many factor, including if the aircraft is doing tankering (i.e. flying with enough fuel to not needing refueling between legs)

This question is too broad. For example, the 757's MLW and MTOW are closer than on most other aircraft, meaning that it can land much sooner after take-off even with full payload and full fuel.

@DeepSpace That would be part of an answer - I allow in the question that it might not be fully answerable.

As asked, this question is only answerable with a huge "it depends".  With a light passenger load & a short flight, it's perfectly common to take off well below the max landing weight.  With a full load & lots of fuel, it may be close to the destination before you're down to max landing weight.  With enough tailwinds & shortcuts, you may arrive at the destination a few hundred pounds above max landing weight (which is generally solved with burning, rather than dumping, the fuel).  But "how long" will it take?  It just depends.

Unless you're asking for a very specific aircraft in a well defined situation, the answer has to be some distance, as there is a multitude of factors involved.
This list is more of a rough collection than anywhere near complete.

First off, if it started with a load already below Maximum Landing Weight (MLW), then no dump is needed. This isn't that unusual, as not every flight is fully loaded - even with tanks full.
Next, MLW is not an absolute value in real life situations, it's a requirement for flight planing
Pilots can decide to land, within reason, with a weight past MLW
The ability to land on a certain Airport depends on the runway length available.
Weight is a combination of fuel tanked and passenger/cargo load, so

With low load, tanks can be full a safe landing can be done without dumping
Similar, with a loaded plane and a partial filled tank (like on short hops)
Or a combination of both, like a series of short hops without taking fuel.

The difference between Maximum Take Off Weight (MTOW) and MLW differs drastic between planes for some it's even the same
There are different fueling strategies depending on airline and destinations.  For a large airliner diference in fuel price can easy accumulate to 30 grand or more.

On international flights fuel price at the destination may be so high compared to the origin that it saves money to fly in with tanks filled up to minimize the amount of fuel to be taken at destination for the flight back. Thus even for a shot distance flight tanks may be all filled up (or at least as much that the planned landing will still work out)
If fuel at destination is comparable (or cheaper), the flight may be done with the minimum fuel necessary.
Same if fuel at the destination is quite cheap, the captain will be ordered to tank as much as possible to return safe.
A plane doing many short hops over a day may load (at some point(s)) as much as possible to reduce time needed for refuelling and increase time flying

Pilots will always try to avoid dumping, as it's literally throwing money out the drain.

... And so on. As said before, there is an almost unlimited number of factors that define the amount of fuel on a plane, its relation to cargo and if a landing with the resulting weight is safe or not. Only if all of these factors add up to the not possible side a dump is to be done.

Angela Merkels failed flight to Argentina in November 2018 makes an interesting example for an extrem combination. The Bundeswehr long haul A340-300E was fully tanked for a ~7,000 nm flight, but still way below MTOW due the light cargo. When the radio failure was detected an hour after start (from Berlin), it returned to Cologne. EDDK got a well sized, almost 4 km long runway, leaving ample space for an overweight landing.

Does it vary so much between aircraft types, distances,
  passenger/cargo weights and other conditions that it's not simply
  possible to say what is typical

This is pretty much the case. For example in a lot of smaller trainer aircraft you are more or less always in the CG range to make a successful landing. On the contrary in larger aircraft fuel burn schedules are extremely important to simply keeping the aircraft airborne.
Dumping fuel is generally not idea from a strictly business standpoint you are basically throwing money out of the aircraft which no airline wants to do on purpose.
What varies heavily between all flights is that at some point its up to humans, and humans make mistakes. Fuel loads may be calculated automatically but some guy still needs to usually shut the pump off at the right time, the pilots need to fly the plane as prescribed and the conditions need to be as expected. Any variable in this could create an issue for you.
For example lets say you take off and get an unexpected tail wind of 100 Kts for the whole ride. Lets also say that you loaded up as much fuel as you could on account of you were flying to a smaller airfield and you were unsure they had enough fuel on hand to get you home. You knew you could bring enough to get there and back but you would be right at the limit of the load config. That 100Kt tail wind is going to save you a fair bit of fuel you intended on burning and due to unforeseen things you may now be over weight.
Now lets say you are flying short haul in a 737, you are doing a 30 min hop and its the end of the day. You have the the required fuel plus reserves so you are flying pretty light. A light passenger load and not much cargo to haul, you may be in range for the whole flight.
Those are just two of a very long list of examples of different load configurations that can lead to always in range, or substantially out of range situations.


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How does experienced pressure vary with airspeed?
Drag increases with the square of airspeed. Is the same true of the pressure that a forward-facing area experiences?
As an aircraft approaches and then exceeds the speed of sound, how does experienced pressure on a forward-facing area increase?

Related: Will control surfaces on a plane be less efficient at a higher altitude?

I don't mean to nit pick, but this is really should be two separate questions.

1) Pressure is simply a force divided by an area, so yes: The dynamic pressure experienced by a forward-facing surface will, in an incompressible flow, vary with the square of the speed.
2) The dynamic pressure increases dramatically as one approaches the speed of sound, once going faster than mach one the pressure will begin to decrease. The trans-sonic phase (around mach one) is difficult to describe and can depend on the airflow around the body - but in many cases it can be quite stable.
-edit-
For the second question here's a couple of links that can provide more information:

Transonic flow around a rocket
NASA history of transonic research

Drag increases with the square of airspeed. Is the same true of the pressure that a forward-facing area experiences?

Drag increases with the square of the airspeed because it is a function of the dynamic pressure $\bar{p}$:
$$D = C_D A \bar{p} =  C_D A \frac{1}{2} \rho V^2$$
So the answer is yes, because the drag is a function of the (dynamic) pressure that a forward-facing area experiences.
I do not speak of the static pressure because that is a function of the atmospheric conditions, and is not a function of the movement of the aircraft through the atmosphere.

As an aircraft approaches and then exceeds the speed of sound, how does experienced pressure on a forward-facing area increase?

I think this has been addressed in the answers here.

to whom has downvoted: care to explain? or should we guess?

The answers to http://aviation.stackexchange.com/questions/25089 don't describe how pressure on a forward-facing area varies with velocity in the transonic/supersonic regimes.